Check access for only the requesting user when determining subscribed status

What does this MR do?

Checks access only for requesting user when checking if subscribed

We don't need to check access for all participants when determining if a single user is subscribed to a Subscribable, only the current user.

By not checking access in bulk we skip instantiating a ProjectTeam and querying for associated members, which is expensive for projects with many members.

#325337 (closed)

Does this MR meet the acceptance criteria?

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